The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: spyke on 01.08. 2009 22:03
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Hi chaps,
If Im using 47 tooth rear sprocket(a65 wheel)on my A10 what size gearbox sprocket would I need to give me normal road gearing?
Cheers Spyke
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Spyke,
You can work it out yourself.
Top gear is 1:1 ratio so gearbox ratios can be discounted.
The first thing to do is find the final ratio which is engine/clutch x gearbox/back sprocket.
My A7 has:
engine - 27 teeth
clutch - 54 teeth
gearbox - 18 teeth
rear hub - 45 teeth
so final ratio is 27/54 x 18/45 which = .2 (five turns of the engine gives 1 turn of the back wheel)
so if you want to fiddle with the final drive sprockets and keep the original gearing you just plug the final ratio into the equation instead of the sprocket you want and work it out.
eg, if I stuck a 20 tooth sprocket on the gearbox the rear hub would be 27/54 x 20/.2 = 50 teeth
and conversly if you stick 50 tooth on the rear hub and want the gearbox its .2 x 50 x 54/27 = 20 teeth.
hope this helps, cheers